Modern Vespa

"Next time," with stripped cases, preheat the case in an oven at 350.

Quick comment about JB Weld:
I've never used it. Not sure if you guys are using that word in a generic sense like Xerox, but there are better epoxies out there.

From trail and considerable error at my day job:
Any epoxy will make a terrible crack repair. It also makes a lousy cap.

With a mechanical bond, it's an excellent plug.
One can get an idea observing older Bondo(another generic) repairs. See where it fails?

Thought about your repair...
"If I were you," I'd have drilled a small hole the size of a syringe tip where you have known holes inside the case. Then injected Uhu Endfest (as used in FMP's video) with a syringe and tape the hole with duct/stucco tape while it cures. Can't imagine how that could fail.

Until my JB 'Welds' fail, I cannot say a bad word about it. Mind you I was meticulous with the prep and build up, and I gave it a long time to set hard and cure at relatively low temperatures. I suspect that if this process is rushed, it will give you trouble down the line. I honestly have no complaints, but understand the superiority of TiG welding done properly.

I'm with you, SWA. I've used JBWeld to good effect numerous times over the years. I don't know why this area failed not just once, but twice. I prepped it like crazy, had lots of overlap of JBWeld with the base metal, and a good, keyed surface.

In any case, it's tight now and I don't see that changing.

However...

After finding an air leak in my base gasket sandwich last night, I re-sealed it and checked it again a little while ago and now have a leak coming up one of the cylinder studs. So I guess I'll be dealing with that next time I'm out in the workshop. Of course.

Weicon Titanium is 2x stronger than JB Weld. Both are knead epoxies.

All products like these have a technical data sheet online somewhere. Kinda tricky comparing metric ASTM standards comparisons to ours!

The Weicon repair stick is twice as strong for this application.

Thanks Ray. I've also tried something called Chemical Metal (maybe a UK brand?) which was not so good. I once used it to bridge an enlarged transfer port on a 177 project and the whole lump just blew out whilst high revving up a long hill. The knead sticks are my least favourite as there tends to be less surface contact, despite them setting rock solid. I find the liquid products are harder to work with because you often have build a 'frame' to contain the stuff while wet, but if you've drilled small holes or scratched the surface as part of the 'keying in' process, nothing seeps into the nooks and crannies like the liquid stuff.

Here are the tech specs for UHU Endfest, I've had great results with Marine JB Weld, but looking at the UHU sheet, I'll he giving it a go!

I'm still curious about aluminum brazing. I asked the question on a metal work forum about it and it sounds doable. I can link to the discussion if you like. I have a case with a welded rotary pad. It doesn't look like TIG, but it's metal and a decent repair.

The UHU is only good to 175F/80C. One advantage of JBWeld is that it's rated to 500F/260C sustained temperature.

Why the hell-bent desire for plastics? We all know that people with the right tools and skills do exist and it's not all that much more expensive especially when all the time doing things two or three times is factored in.

1) Having someone else weld it increases cost by probably 20x versus the cost of some JBWeld or other epoxy
2) I started this thread because I'm trying to gain the skills to use the tools to do this "right" myself.

Anyone who didn't shoot out of their mom wearing a welder's mask and holding a torch was at this same basic point in their journey to learning any moderately complex skill. Throwing rocks when people are sharing their experiences of trying to learn is just being an asshole.

Yes, I see.

I would love to be able to weld…

Who doesn't want to be their own master??

Props for trying…

My take on this is that the jury is still out on the use of chemical metal vs real metal. If done properly, I honestly do not see JB Weld as inferior, just a different approach, and one which is more accessible to those of us without welding experience, equipment or deep pockets. Something which is 'good enough' doesn't need to be the best. A work colleague used to say "the best is the enemy of the good" ie. if we always strive for the best, we're going to miss a lot of good things along the way

That's a generalized heat rating. Depends on the application. One could also bump up heat resistance by adding less hardener. 2 parts resin to 1 part hardener.

That's really interesting. I had no idea this was an option. I assume there's a tradeoff, though. Do you know if it impacts strength, or just extends the cure time?

I also recall when I was doing my boat I spaced out at one point and only added 20% of the recommended hardener to the resin on a batch of West System. That never did cure, so I had to scrape it all off.

I would stick to what we know and works…

JB weld… 1 part to 1 part…

And 500F heat resistance sounds pretty good…

I'm happy with JBWeld. It's historically done right by me, plus is reasonably cheap and easily available.

Next time, when I'm working preventatively and under more favorable circumstances, I think this whole experience will be much smoother.

I will probably still layer in JBWeld on the inside of the ports if I break through into the new metal and can see pores, but don't expect anything on the order of what I went through getting this repair across the line.

(BTW, it held air and is now re-assembled)

I also upped the port timings while I had it apart, and the gasket sandwich was the cause of the last couple air leaks, so yet another self-inflicted wound just to keep the adventure consistent.

Epoxies are kind of counter-intuitive. Adding more hardener doesn't produce a harder result. Too little, as in your case, doesn't either -- though I imagine if you mixed that ratio well it would have eventually hardened!

Take Uhu as an example. It's a user-friendly product that covers a variety of applications. One could plug one of the tubes and dispense more resin (2 to 1 by weight) and get a harder, more temperature/chemical resistant result -- I think that's what FMP does in his video(?). It'll take longer to cure for sure, but that also provides better penetration into pores and dremel keying.

A quick update now that I've been back on the road for ten days or so.

I did two things as long as I was taking things apart and putting them back together. First, I fixed a slight lip, maybe 1.5mm, where the base of the exhaust port was higher than the cylinder at BDC. That seems to have reduced the temps at WOT pretty significantly, like from pushing 350F down to 330F at WOT.

I raised the ports by .5mm (swapped a head gasket for a base gasket), taking the transfer timings up to 129 to see if they'd be too much for the ol' PM Tuning pipe. Turns out they were, but not terribly.

It has a little less power, but more annoyingly, the power band moved up enough that it struggles to run at 55 MPH or so in 4th, so I had to shift and then downshift more than I normally would have on that stretch of road.

Eventually I'll get back to it and drop the cylinder back down, but in the meantime, I'm liking the cooler highway running temps, even if the performance isn't as good as it was. A worthwhile experiment when all is said and done.

CM, did you look at rejetting after moving the base/head gasket?

Every time I played around with the gasket heights, always ended up moving the needle and/or main jet up or down 1 size (still using the pwk?)…